Systems and methods presently are used for the automatic or semi-automatic control of process gas distribution in semi-conductor manufacturing. One such system and method which is highly advantageous is shown in U.S. patent application Ser. No. 194,828, filed May 17, 1988, now U.S. Pat. No. 4,989,160, which is assigned to the assignee of this patent application. Despite its excellence, further improvements are needed to solve several remaining problems.
Some prior systems provide for remote control at a single computer console of a large number of remote gas flow control units or "cabinets". Each control unit controls the delivery of process gas to one or more locations where the gas is used to make semiconductor devices. These locations are called "tool" locations. Most control units are located relatively far from the tool locations. It is desired to provide communication links between the tool locations and the flow control cabinets and to provide means for monitoring and controlling the units at a central location. The problem is how to do this without excessive cost.
Another problem with prior systems and methods has been caused by the need to re-calibrate transducers in the gas flow control cabinets at periodic intervals. For example, it has been customary to zero-calibrate pressure transducers once every three to six months or so. The process used in the past often has required up to a full day of labor by one worker for each cabinet. This creates relatively high labor costs and shuts the control unit down for a substantial time during which it cannot be used for production.
A further problem has been created by the expansion of the capabilities of each of the gas flow control cabinets so that it can deliver gas to any one or more of several different tool locations upon demand. This has created problems in purging the gas lines of toxic gas for worker safety during local maintenance of the flow control units. If the "flow-through" process is used, where a purge gas such as nitrogen simply is pumped in one direction through the delivery conduit, it must flow through the long conduit from the cabinet to the tool. This is wasteful of expensive gas, and wastes time. Furthermore, sometimes it is not possible to use the flow-through process, in which case maintenance work on the long delivery conduit can be hazardous. The problems, then, are how to achieve safe local purging without incurring excessive costs, and how to purge the long delivery conduit when flow-through purging is not available.
A similar problem in purging the conduits has been created by the addition of means for delivering gas selectively from two different supply tanks and switching back and forth between the two tanks.
Each of the gas flow control cabinets has an exhaust outlet which is connected to an exhaust duct and from which air and gas from the inside of the cabinet is exhausted at a relatively high flow rate in order to avoid the accumulation of toxic gas in the cabinet due to leaks, etc. Flow measurement means are provided to measure the flow rate of the exhaust gas. If the flow rate falls below a pre-determined safe level, an alarm is activated so that the low flow condition can be remedied. Usually, each duct and fan is in place in the plant before the cabinet is installed. If the diameter of the duct is not the same as that of the exhaust outlet, the flow rate measurement will be erroneous. A tedious and expensive firmware program adjustment then is required in order to avoid this source of error. The labor cost and time to do this constitute another problem to be solved.
A further problem in prior gas distribution systems is that sometimes it is necessary to change the association between a tool location and the gas distribution conduits. For example, it may become necessary to supply a given tool with a different gas or mix of gases, and it may be necessary or expedient to change the connection of different gas distribution conduits to the tool. In the past, this has required re-wiring of the electrical connections so that the tool is correctly connected to the proper control unit or units corresponding to the new gas conduit connections. The inventors have recognized that the re-wiring requirement is costly and time-consuming; it increases equipment down-time and reduces productivity.